The light source of the daylight of a standard D illuminant for a standard light source color matching observation box or light box in the current market includes a variety of brands of fluorescent tubes and uses a halogen tungsten lamp to pass through the light filter so that the radiated light ray simulates a D illuminant specified by the CIE standard. The relative spectral power distribution of the radiated light source passing through the light filter with the halogen tungsten lamp can reach A level of the metamerism index of the D illuminant specified by the CIE standard. However, due to the influence of the material and the manufacturing process technology, it is difficult for the technical indicator of the relative spectral power distribution of its function for irradiating the light source to achieve the A-level metamerism index quality level <0.2 of the CIE D-standard illuminant. In the course of the using for a long time, it will gradually deteriorate, and even exceed the metamerism index of 0.25, with only B level of >0.25˜0.50 level. As the halogen tungsten lamps of the same specification have a difference in material composition, the relative spectral power distribution of the light emitted therefrom cannot have a stable quality. The configured light filter of colored optical glass will vary with the relative spectral power distribution of the permeable radiated light because of material. The combination of a light filter and a halogen tungsten lamp can only form a CIE standard D illuminant of a single specification. The CIE standard illuminant includes D65, D75, D55, D50 and other standards. The prior art makes it difficult to ensure that the standard light source continues to have a stable spectral power distribution after prolonged use, and the replacement of the halogen tungsten lamp or the light filter will produce a difference, thus affecting the accuracy of the test.
It is difficult for the spectral power distribution of the light ray of the halogen tungsten lamp through the light filter to solve the zigzag shape of different wavelengths, so the light source quality of SpectraLightQC standard light source color matching observation box (new products put into market only in 2013) which is considered to have the highest quality in the current market can only reach A or B level of 0.20-0.30 according to the metamerism index of the light source of the quality indicator specified by CIE15: 2004. The halogen tungsten lamp tube used by such standard D daylight source causes the relative spectral power distribution of the light source to vary since the used tungsten wire and the inert gas containing halide and halogen elements has a gradual change in efficiency in the process of using the lamp tube for a long time and the material (chemical material) of the colored optical glass for the light filter varies. Therefore, in the course of use, the metamerism index of the light source gradually increases from 0.21 to 0.25-0.30, and can only be maintained at the B level. Although the illumination is still high, the luminous area formed by winding tungsten wires in the lamp tube has a difference in distances of different lengths, and the illumination energy emitted thereform will be different, so the illumination uniformity for the position storing objects in the light source box can only reach about 90% of the quality level.
In recent years, due to LED light source has the advantages such as saving power, high luminous efficiency and long life, etc., a number of light source research units have introduced the use of an LED to simulate the CIE standard D light source. Since the spectral distribution of the light ray emitted by the LED can only be in the narrow-wavelength band, and the main peak of the spectrum emitted by each LED is narrowed into spikes, although the light rays of three narrow-waves of red, green and blue can form an integrity to emit white light, its spectral power distribution has defects. So a multi-stage narrow-band LED is used to combine to emit light to illuminate the spectral power distribution close to the specification requirements of the D illuminant specified by the CIE standard, but the relative spectral power distribution of the light ray that it illuminates the position in which objects are stored in the standard light source color matching observation box is non-uniform. Recently an LED-based intelligent color matching light box is introduced, using the method of using at least with an LED white light source and a plurality of single-color LEDs as the illuminant. A halogen tungsten lamp is used to configure a special light filter to emit light to supplement the radiant energy of the overall visible light. The use of electronic technology to monitor the intelligent adjustment of the energy of the light ray emitted by each LED light. Although the combination of light ray emitted therefrom can simulate the color temperature index of the CIE standard D illuminant, the main peak energy of the spectrum of the light ray emitted by a variety of LEDs, and the relative spectral power distribution parameters of the light ray emitted therefrom cannot reach the index of each band specified by the CIE standard. It is clear that the difference is very obvious only if the measured data for analyzing the relative spectral power distribution of the emitted light ray and the relative spectral power distribution parameter of the D illuminator specified by the CIE standard are compared. Although the current general color temperature measuring instrument is used to measure its color temperature value so as to achieve the D light source indicators specified by the CIE standard, it is very difficult for the metamerism index of the light source emitted therefrom to reach A level. This uses a plurality of single-color LEDs to configure a white light LED as the main body of the light source radiation energy, but the light ray transmitted in such a way that a tungsten lamp configures a light filter is used as a supplement of the radiation energy. It is still very difficult for the radiation uniformity to have a good uniformity on the surface of the sample to be measured.